[PATCH v6 2/4] git-cherry-pick: Add keep-redundant-commits option

[Neil Horman <nhorman@tuxdriver.com>]

The git-cherry-pick --allow-empty command by default only preserves empty
commits that were originally empty, i.e only those commits for which
<commit>^{tree} and <commit>^^{tree} are equal.  By default commits which are
non-empty, but were made empty by the inclusion of a prior commit on the current
history are filtered out.  This option allows us to override that behavior and
include redundant commits as empty commits in the change history.

Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
---
 Documentation/git-cherry-pick.txt |   12 ++++-
 builtin/revert.c                  |    8 +++-
 sequencer.c                       |   97 ++++++++++++++++++++++++++++++++-----
 sequencer.h                       |    1 +
 4 files changed, 103 insertions(+), 15 deletions(-)

diff --git a/Documentation/git-cherry-pick.txt b/Documentation/git-cherry-pick.txt
index 730237a..0c004e9 100644
--- a/Documentation/git-cherry-pick.txt
+++ b/Documentation/git-cherry-pick.txt
@@ -110,7 +110,17 @@ effect to your index in a row.
 	behavior, allowing empty commits to be preserved automatically
 	in a cherry-pick. Note that when "--ff" is in effect, empty
 	commits that meet the "fast-forward" requirement will be kept
-	even without this option.
+	even without this option.  Note also, that use of this option only
+	keeps commits that were initially empty (i.e. the commit recorded the
+	same tree as its parent).  Commits which are made empty due to a
+	previous commit are ignored.  To force the inclusion of those commits
+	use `--keep-redundant-commits`.
+
+--keep-redundant-commits::
+	If a commit being cherry picked duplicates a commit already in the
+	current history, it will result in an empty changeset.  By default these
+	redundant commits are ignored.  This option overrides that behavior and
+	creates an empty commit object.  Implies `--allow-empty`.
 
 --strategy=<strategy>::
 	Use the given merge strategy.  Should only be used once.
diff --git a/builtin/revert.c b/builtin/revert.c
index 06b00e6..f135502 100644
--- a/builtin/revert.c
+++ b/builtin/revert.c
@@ -115,13 +115,15 @@ static void parse_args(int argc, const char **argv, struct replay_opts *opts)
 		OPT_END(),
 		OPT_END(),
 		OPT_END(),
+		OPT_END(),
 	};
 
 	if (opts->action == REPLAY_PICK) {
 		struct option cp_extra[] = {
 			OPT_BOOLEAN('x', NULL, &opts->record_origin, "append commit name"),
 			OPT_BOOLEAN(0, "ff", &opts->allow_ff, "allow fast-forward"),
-			OPT_BOOLEAN(0, "allow-empty", &opts->allow_empty, "preserve empty commits"),
+			OPT_BOOLEAN(0, "allow-empty", &opts->allow_empty, "preserve initially empty commits"),
+			OPT_BOOLEAN(0, "keep-redundant-commits", &opts->keep_redundant_commits, "keep redundant, empty commits"),
 			OPT_END(),
 		};
 		if (parse_options_concat(options, ARRAY_SIZE(options), cp_extra))
@@ -139,6 +141,10 @@ static void parse_args(int argc, const char **argv, struct replay_opts *opts)
 				"--abort", rollback,
 				NULL);
 
+	/* keep_if_made_empty implies allow_empty */
+	if (opts->keep_redundant_commits)
+		opts->allow_empty = 1;
+
 	/* Set the subcommand */
 	if (remove_state)
 		opts->subcommand = REPLAY_REMOVE_STATE;
diff --git a/sequencer.c b/sequencer.c
index 71929ba..acc9c6d 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -13,6 +13,7 @@
 #include "rerere.h"
 #include "merge-recursive.h"
 #include "refs.h"
+#include "argv-array.h"
 
 #define GIT_REFLOG_ACTION "GIT_REFLOG_ACTION"
 
@@ -251,6 +252,30 @@ static int do_recursive_merge(struct commit *base, struct commit *next,
 	return !clean;
 }
 
+static int is_index_unchanged()
+{
+	unsigned char head_sha1[20];
+	struct commit *head_commit;
+
+	if (!resolve_ref_unsafe("HEAD", head_sha1, 1, NULL))
+		return error(_("Could not resolve HEAD commit\n"));
+
+	head_commit = lookup_commit(head_sha1);
+	if (!head_commit || parse_commit(head_commit))
+		return error(_("could not parse commit %s\n"),
+			     sha1_to_hex(head_commit->object.sha1));
+
+	if (!active_cache_tree)
+		active_cache_tree = cache_tree();
+
+	if (!cache_tree_fully_valid(active_cache_tree))
+		if (cache_tree_update(active_cache_tree, active_cache,
+				  active_nr, 0))
+			return error(_("Unable to update cache tree\n"));
+
+	return !hashcmp(active_cache_tree->sha1, head_commit->tree->object.sha1);
+}
+
 /*
  * If we are cherry-pick, and if the merge did not result in
  * hand-editing, we will hit this commit and inherit the original
@@ -258,26 +283,67 @@ static int do_recursive_merge(struct commit *base, struct commit *next,
  * If we are revert, or if our cherry-pick results in a hand merge,
  * we had better say that the current user is responsible for that.
  */
-static int run_git_commit(const char *defmsg, struct replay_opts *opts)
+static int run_git_commit(const char *defmsg, struct replay_opts *opts, int empty)
 {
-	/* 7 is max possible length of our args array including NULL */
-	const char *args[7];
-	int i = 0;
+	struct argv_array array;
+	int rc;
+	int index_unchanged = is_index_unchanged();
+
+	/*
+	 * if index_unchanged is < 0, then we encountered an error
+	 * trying to parse HEAD or the active_cache_tree, so bail out
+	 */
+	if (index_unchanged < 0)
+		return index_unchanged;
+
+	if (!empty && !opts->keep_redundant_commits && index_unchanged)
+			/*
+			 * The head tree and the index match
+			 * meaning the commit is empty.  Since it wasn't created
+			 * empty (based on the previous test), we can conclude
+			 * the commit has been made redundant.  Since we don't
+			 * want to keep redundant commits, we can just return
+			 * here, skipping this commit
+			 */
+			return 0;
+
+	argv_array_init(&array);
+	argv_array_push(&array, "commit");
+	argv_array_push(&array, "-n");
 
-	args[i++] = "commit";
-	args[i++] = "-n";
 	if (opts->signoff)
-		args[i++] = "-s";
+		argv_array_push(&array, "-s");
 	if (!opts->edit) {
-		args[i++] = "-F";
-		args[i++] = defmsg;
+		argv_array_push(&array, "-F");
+		argv_array_push(&array, defmsg);
 	}
+
 	if (opts->allow_empty)
-		args[i++] = "--allow-empty";
+		argv_array_push(&array, "--allow-empty");
+
+	rc = run_command_v_opt(array.argv, RUN_GIT_CMD);
+	argv_array_clear(&array);
+	return rc;
+}
 
-	args[i] = NULL;
+static int is_original_commit_empty(struct commit *commit)
+{
+	const unsigned char *ptree_sha1;
 
-	return run_command_v_opt(args, RUN_GIT_CMD);
+	if (parse_commit(commit))
+		return error(_("Could not parse commit %s\n"),
+			     sha1_to_hex(commit->object.sha1));
+	if (commit->parents) {
+		struct commit *parent = commit->parents->item;
+		if (parse_commit(parent))
+			return error(_("Could not parse parent commit %s\n"),
+				sha1_to_hex(parent->object.sha1));
+		ptree_sha1 = parent->tree->object.sha1;
+	} else {
+		ptree_sha1 = EMPTY_TREE_SHA1_BIN; /* commit is root */
+	}
+
+	return !hashcmp(ptree_sha1, commit->tree->object.sha1);
 }
 
 static int do_pick_commit(struct commit *commit, struct replay_opts *opts)
@@ -289,6 +355,7 @@ static int do_pick_commit(struct commit *commit, struct replay_opts *opts)
 	char *defmsg = NULL;
 	struct strbuf msgbuf = STRBUF_INIT;
 	int res;
+	int empty_commit;
 
 	if (opts->no_commit) {
 		/*
@@ -414,6 +481,10 @@ static int do_pick_commit(struct commit *commit, struct replay_opts *opts)
 		free_commit_list(remotes);
 	}
 
+	empty_commit = is_original_commit_empty(commit);
+	if (empty_commit < 0)
+		return empty_commit;
+
 	/*
 	 * If the merge was clean or if it failed due to conflict, we write
 	 * CHERRY_PICK_HEAD for the subsequent invocation of commit to use.
@@ -435,7 +506,7 @@ static int do_pick_commit(struct commit *commit, struct replay_opts *opts)
 		rerere(opts->allow_rerere_auto);
 	} else {
 		if (!opts->no_commit)
-			res = run_git_commit(defmsg, opts);
+			res = run_git_commit(defmsg, opts, empty_commit);
 	}
 
 	free_message(&msg);
diff --git a/sequencer.h b/sequencer.h
index e2cd725..aa5f17c 100644
--- a/sequencer.h
+++ b/sequencer.h
@@ -30,6 +30,7 @@ struct replay_opts {
 	int allow_ff;
 	int allow_rerere_auto;
 	int allow_empty;
+	int keep_redundant_commits;
 
 	int mainline;
 
-- 
1.7.7.6